//class
//建立class需要的集合模型对象
let mongoose = require('mongoose');
let Classname = new mongoose.Schema({
    name: String
  })
  //class删除集合模型对象
  let classdelate = new mongoose.Schema({
    name: String
  }) 
   //建立class与模型的关系
 let classModel=mongoose.model('classModel', Classname, 'class');
  //class删除模型关系
  mongoose.model('classdelateModel', classdelate, 'class');
  //class add模型
  let classaddModel=mongoose.model('classaddModel', classdelate, 'class');